1. Field of the Invention
The present invention relates to a method and apparatus for configuring a transport block size for a user equipment in a wireless communications system, and more particularly to a method and apparatus for configuring a transport block size for a user equipment in a high speed downlink packet access (HSDPA) system with 64 quadrature amplitude modulation (64QAM) or higher order modulation capability.
2. Description of the Prior Art
The third generation (3G) mobile telecommunications system has adopted a Wideband Code Division Multiple Access (WCDMA) wireless air interface access method for a cellular network. WCDMA provides high frequency spectrum utilization, universal coverage, and high quality, high-speed multimedia data transmission. The WCDMA method also meets all kinds of QoS requirements simultaneously, providing diverse, flexible, two-way transmission services and better communication quality to reduce transmission interruption rates. Through the 3G mobile telecommunications system, a user can utilize a wireless communications device, such as a mobile phone, to realize real-time video communications, conference calls, real-time games, online music broadcasts, and email sending/receiving. However, these functions rely on fast, instantaneous transmission. Thus, targeting at the third generation mobile telecommunication technology, the prior art provides High Speed Package Access (HSPA) technology, which includes High Speed Downlink Package Access (HSDPA) and High Speed Uplink Package Access (HSUPA), to increase bandwidth utility rate and package data processing efficiency to improve uplink/downlink transmission rate.
For a user equipment (UE) in HSDPA, physical channels include a high speed physical downlink shared channel (HS-PDSCH) for transferring payload data, and a high speed physical control channel (HS-DPCCH) for uploading an acknowledgement/negative acknowledgement (ACK/NACK) and a channel quality identifier (CQI). As for the media access control (MAC) layer of the HSDPA UE, a MAC-(e)hs entity utilizes a transport channel of a High Speed Downlink Shared Channel (HS-DSCH) for receiving data from the physical layer. In addition, a shared control channel for HS-DSCH (HS-SCCH) is used as a physical downlink channel, responsible for transmission of control signals corresponding to HS-DSCH, such as UE identities, channelization code sets, modulation schemes and transport block sizes, so that the UE can correctly receive data packets from HS-DSCH.
In HSDPA, two parameters are used to determine transport block (TB) sizes. One parameter is a Transport Format and Resource Indicator (TFRI) value carried in the second and the third slots of HS-SCCH, which is represented by ki and ranges from 0 to 63. The other is a k0,i value corresponding to a combination of a modulation scheme and a number of channelization codes chosen by the Node B, which can be determined by reading information of channelization code sets and modulation schemes carried in the first slot of HS-SCCH. Thus, a combination table is provided for the UE to map a combination of the chosen modulation scheme and the number of channelization codes to the k0,i value. A sum of the TFRI and the k0,i forms another index kt for determining actual TB sizes through the mapping of a transport block size table.
Please note that, the 3rd Generation Partnership Project (3GPP) newly introduces a combination table and a transport block size table in the aforementioned MAC protocol specification to support a high speed downlink packet access (HSDPA) system with 64 quadrature amplitude modulation (64QAM) capability, in which the range of TB sizes is enlarged for significantly enhancing data transmission rate.
However, since the k0,i value corresponding to a least resource usage in the combination table is larger than the index kt corresponding to a smallest TB size in the transport block size table, the smallest TB size cannot be used for data reception in the HSDPA system, so that waste of radio resources may occur. More specifically, since the least resource usage k0,i value (i.e. the minimum k0,i value ) in the combination table is 20, which corresponds to a combination of Quadrature Phase Shift Keying (QPSK) modulation and one channelization code usage, the minimum index kt capable of being formed by ki and k0,i is also 20 (i.e. kt=k0,i+ki=20+0=20), so that smaller TB sizes corresponding to index kt from 0 to 19 in the transport block size table cannot be used for data reception in the HSDPA system. In this case, the waste of radio resources may occur in some situations. For example, if the network side only has 130 bits of data for transmission, since the smallest TB size capable of being used is the size of 272 bits corresponding to 20 of the index kt, the length of padding bits in the being-transmitted TB will be up to 142 bits, which is even more than the transmitted data, resulting in the waste of radio resources.
In short, since the prior art cannot use smaller TB sizes for data reception, the waste of radio resources may occur.